It now is common in the manufacture of plastics articles to supply the extruder with a combination of base or virgin material and scrap material such as that created by the trimming and finishing of previously extruded products. Apparatus for mixing scrap and base materials for subsequent discharge to an extruder is disclosed in application Ser. No. 638,911, filed Dec. 8, 1975. The base or virgin material conventionally is in the form of dense, solid pellets which are readily fluent, whereas the scrap material is chopped or ground film that is rather fluffy, relatively non-fluent, and less dense than the base material. The ability of the base material to flow makes it possible to feed the base material without reliance on a driven feed mechanism, such as an auger, but the fluffiness of the ground scrap, coupled with its lower density, usually necessitates the use of positive feed means to effect movement of the scrap material. The grinding, chopping, and movement of the scrap material quite often causes the latter to acquire a static electrical charge which further interferes with the free flow of the scrap material. Thus, when the scrap is accumulated in the hopper from which it subsequently is to be discharged, it is not uncommon for the pieces of scrap material to form a bridge adjacent the bottom of the hopper and interfere with the movement of scrap out of the hopper.
To prevent bridging of scrap material adjacent the bottom of a hopper it has been proposed heretofore to utilize agitating arms which rotate within the hopper. Such arms conventionally are rotated about a vertical axis and are inclined to such axis at an angle corresponding to the taper of the hopper. Although such agitating arms do facilitate the downward flow of scrap through the hopper, they result in establishment of what may be termed a head of scrap extending upwardly from the bottom of the hopper. A substantial weight of scrap material thus may occupy the hopper and if such scrap is fed from the hopper horizontally, rather than vertically, substantial heat can be generated in effecting horizontal discharge of the scrap. The generation of heat is objectionable because it may result in liquification of the scrap material in the hopper.
The simultaneous introduction of scrap and base plastics materials into a mixing or blending chamber also presents problems due to the difference in densities between the base and scrap materials, particularly if the scrap is fed into the base material. That is, if the less dense scrap is fed into a column of denser base material, the force required to displace the denser material with the less dense material results in the generation of heat which may effect premature liquification of the less dense material.